The present invention relates generally to apparatus that allows access to the vascular system of a human (or other animal) for the high-volume fluid flow required in hemodialysis, plasmapheresis, and other fluid exchange therapies. More particularly, the present invention relates to a septum-less subcutaneously implanted access of single- or dual-lumen construct and a mating needle apparatus.
There exists a class of devices for accessing fluid spaces and vessels within a human (or animal) body that are generally referred to as xe2x80x9cportsxe2x80x9d. Herein, xe2x80x9cvesselxe2x80x9d is defined as any conduit carrying a fluid within the patient""s body. These prior art devices comprise a chamber having an access opening sealed by means of a septum and having an egress from a second location leading to a catheter disposed within a fluid space or vessel. The septum allows a needle to pass into the chamber, but then closes when the needle is removed, thereby preventing fluid leakage from within a space or vessel and also anything from entering or exiting the chamber. These devices are usually implanted below the skin to prevent infection, other contamination, and mishandling.
Ports are designed for relatively infrequent use, perhaps once a week, and, importantly, for flowrates of 50 milliliters per minute or less, as is common during chemotherapeutic treatment. Modification of these devices for hemodialysis, plasma-pheresis, and other fluid exchange therapies, which require much greater flowrates, by simply enlarging the device components, poses several serious drawbacks that effectively limit use in such applications. First, the septum degrades quickly due to the larger gauge needles necessary to accommodate the flowrates required in hemodialysis. Repeated puncturing of the septum by these large needles produces numerous free-floating septum fragments that can find their way into the circulatory system. Accordingly, the useful life of the devices is substantially shortened, thereby defeating one of the purposes of using an implanted subcutaneous device. Second, the flowpath has several stagnation points where clots may form and also is not completely flushable or easily cleaned, thereby providing breeding grounds for infection, once contaminated or a build-up of material which may adversely affect function. Third, the flowpath is not streamlined and contains flowpath obstructions, sharp corners, and abrupt changes in flow area and flow direction. This tends to increase the shear stress and turbulences experienced by blood flowing through the device due to the significantly higher flowrates required in hemodialysis, thereby increasing erythrocyte damage and platelet activation. Also, the tortuous flowpath increases the pressure drop through the devices, which can increase air release and foaming, causing the dialysis machine""s safety alarms to activate.
Typical access port apparati are disclosed in U.S. Pat. No. 5,180,365 (Jan. 19, 1993), U.S. Pat. No. 5,226,879 (Jul. 13, 1993), U.S. Pat. No. 5,263,930 (Nov. 23, 1993), and U.S. Pat. No. 5,281,199 (the ""199 patent) (Jan. 25, 1994); all entitled xe2x80x9cIMPLANTABLE ACCESS DEVICESxe2x80x9d and all issued to William D. Ensminger as either the sole or the first-named inventor. Only the ""199 patent is assigned, that assignment being to Michigan TransTech Corporation of Ann Arbor, Mich. The following discussion concerns the (assigned) ""199 patent; while all of the references are relevant, the ""199 patent embodies the most recent material and also incorporates material from each of the earlier patents.
The devices described in the ""199 patent include a funnel-shaped entrance to an access housing, which is fixed to the surrounding tissue. The housing is connected to an articulated valve, which is in turn joined to a catheter. Several types of valves are disclosed, including one that is a tube fabricated in a flattened shape that is forced open by the insertion of a filament. Other valves disclosed include manually activated types. In these manual valves, manual actuation applied to the skin and translated to the device moves two disks which slide over and in contact with each other to align holes in those disks. A needle may be inserted when the holes are aligned; the disks secure the needle in the housing when the external manual pressure is released. This patent also discloses a curved entry (presumably to allow the needle to enter at a convenient angle to the skin but still align parallel to the vessel). The disclosure of this patent, in column 9, line 53, mentions use in hemodialysis treatment.
The Ensminger et al. ""199 device has several characteristics which lead to problems. First, in most embodiments the curved needle must be flexible, and as such can kink or otherwise restrict flow. However, when the needle is inserted, no such kink can be seen by the operator, and may not be detected before damage to the patient results. Another drawback of these devices can best be seen by inspection of FIG. 1A of the ""199 patent, showing an abrupt change in flow diameter where the catheter 46 is joined to the valve 24. Abrupt changes form space for fluid stagnation to occur and/or eddy currents that promote clot formation. Further, such spaces are not easily flushed due to the lack of a streamlined flowpath. This same problem is shown in FIG. 1A of this patent in the stagnant space around the leaf valves 38. Indeed, such problems exist at nearly every transition point between the various structures and assemblies of the ""199 device.
A further drawback of the ""199 device is the attachment of the housing to the surrounding tissue. Since the housing cannot move to accept a rigid needle, the needle must be closely aligned with the port entrance. Otherwise, the needle must be moved transversely under the skin causing discomfort for the patient. Ensminger et al. required the use of a flexible tube to solve this problem. A still further drawback of the ""199 apparatus is shown in FIGS. 41-43. These drawings show needle points where the flow has a radial direction component as it leaves the needle. This change of direction, especially under high flowrates, can severely damage hematocytes and activate platelets. Also, the flexible tube will have a greater flow resistance and higher shear than a rigid straight needle having a similar outside diameter.
A general limitation in all relevant prior art devices is the lack of a streamlined flowpath. Without such streamlining, stagnant volumes exist where clots may form and shear stress is higher, tending towards erythrocytic damage. Such locations cannot be flushed or easily cleaned. Blood residue remaining in the devices after flushing may clot and provide breeding grounds for infection, once contaminated. In addition, pressure drops and abrupt flow direction changes may damage blood components.
The Ensminger ""199 device is still further limited by its lack of effective sealing provisions. There is no force urging the valve to seal. The valve is therefore not fault-tolerant and particles, clots, skin fragments, and imperfections on the inside surface of the valve will cause leakage. In addition, the valve opens in response to very low changes in pressure. Further, the seal is in line with the housing, making the device longer and increasing the changes in pressure experienced by fluids passing through the device. Finally, there is no locking mechanism whereby the needle may be secured to the device.
Accordingly, it is an object of this invention to overcome the above illustrated inadequacies and problems of extant devices by providing a totally implantable access means suitable for repeated use in applications (e.g., hemodialysis with blood flowrates of 250 milliliters per minute or more yet with low pressure drops along the flowpath.
It is another object of this invention to provide a laminar flowstream, even during flow diameter transitions.
It is a further object to provide means where the flowpath is streamlined and provides substantially no stagnation points, and also to provide an apparatus where the entire flowstream is flushable.
It is a still further object of this invention to provide apparatus suitable for single- and dual-lumen catheter systems.
It is yet another object of this invention to provide an access housing that is less painful during needle insertion and more accommodating during dialysis for the patient.
It is a further object to secure the needle within the access housing during the dialysis session.
It is another object of the invention, when using dual-lumen catheters to secure both needles to each other.
It is a still further object to have lower clotting, stenosis, and infection rates than synthetic grafts.
It is yet another object to have lower infection and lumen clotting than percutaneous catheters.
The foregoing objects are met by a subcutaneously implantable device for accessing a vessel within a patient""s body, the device including (a) an access guidance means having a through channel and (b) a catheter having a through channel and comprising an access portion, a sealing portion, and a distal portion. A resilient means for sealing is arranged within the sealing portion of the catheter. The resilient means for sealing ordinarily prohibits fluids from passing the seal. But when a mechanical device is inserted percutaneously, and guided to the catheter""s access portion by the access guidance means, the mechanical device passes through the access portion of the catheter, engages the sealing means, and pushes it open. This provides access to the catheter""s distal portion and, ultimately, the vessel lumen, as the distal portion of the catheter, distal from the access guidance means, extends into a vessel lumen. The catheter is attached to the surrounding tissue supporting the catheter, but the access guidance means""s position is not fixed relative to the tissue.
The means for sealing includes, in a preferred embodiment, a tube made of a resilient material, which incorporates a valving feature within the tube lumen. The tube is disposed axially along the inner wall of the channel. A spring clamp is provided adjacent to and external of the tube and acts to compress the tube such that the tube""s inner lumen is closed, thereby preventing fluids from passing.
The spring clamp is arranged and constructed to close the tube""s lumen such that the longitudinal transition profile from the open to the closed position forms a particular shape. The shape of the valve allows for the conical point of the needle obdurator to open or push apart the rubber valve slit in a wedging action as the needle is pushed through the seal. The needle pushing force overcomes the spring biasing force and the seal""s internal stresses as the needle enters the sealing area without cutting the rubber. Because no cutting occurs, no rubber particles are generated, as seen with septa in ports. Furthermore, the number of penetration cycles to failure is very high, as negligible damage occurs during penetration.
The flowpath transitions between the needle, the tube lumen, and a catheter are arranged and constructed to provide for maximum smoothness and continuous flowpaths without abrupt changes in flow diameter and only gentle changes in flow direction. All narrowing and broadening of the flowpath is gradual, with angles of 25 degrees or less.
The invention also provides for a hollow needle apparatus that matingly corresponds to the through channel of the access device, and an obdurator that is inserted into the lumen of the needle, filling the lumen. This needle/obdurator combination provides a needle assembly with a pointed end, and an outer surface having smooth transitions, which are formed to puncture tissue easily and to open the valve without damaging it.
The needle apparatus further includes a circumferential groove formed into a sector of the needle""s outer surface of approximately 180xc2x0. A spring lock is positioned within the access housing channel upstream from the resilient sealing means, engaging the groove to secure the needle to the access device when the needle is in the correct axial position. The groove and spring lock are designed to disengage when the needle is rotated approximately 90xc2x0, allowing the needle to be extracted from the housing.
Another preferred sealing means includes a fixed axial seating mount affixed to the through hole inner wall distally from said sealing location, the seating mount having passages to allow fluid to pass. A movable valve poppet is upstream from and fixed to said seating mount to prevent radial movement yet allow axial movement of the needle. A compression spring in said seating mount acting on said movable valve poppet provides a force pushing said valve poppet longitudinally against a valve seat. The movable valve poppet is designed with a surface that mates with a surface on the tube""s inner wall (i.e., valve seat). A seal is provided between the mating surfaces of the tube inner wall and the movable valve poppet, such that the spring biasing force pushes the two mating surfaces together and the seal therebetween prevents flow from passing. The movable valve poppet has a proximally facing surface designed to engage the needle. Pushing the needle into the device""s flowpath against the poppet, which overcomes the spring force, moving the poppet away from the sealing surface, thereby opening the valve sealing means and allowing fluid to pass through the access. The needle may be secured in the device by the groove and locking means arrangement, as described earlier.
Another sealing means includes a resilient balloon adjacent to the through channel. The balloon has a septum suitable for penetration by a fine needle. A fluid is introduced through the fine needle to inflate the balloon. The inflated balloon traverses the through channel, contacting the opposing side of the through channel, and thereby closing said hole and preventing any liquids from passing. Alternatively, the balloon may be arranged around the circumference of the through channel, and closes the through channel when inflated.
The presently claimed access device is suitable for both single-needle and standard hemodialysis, plasma-pheresis, and fluid exchange therapy applications. For standard applications, which require two flowpaths, the housing may be arranged and constructed to engage two needle assemblies, as described above, and include dual-lumen through channels. When two needles are used, a spring-loaded bar may be provided that engages each needle, thereby locking both needles to each other to preclude inadvertent disconnection of only one needle, thereby enhancing patient safety.
It is important to note that the primary object of this invention is to provide an implantable, subcutaneous access device suitable for applications requiring flow rates of 250 ml/min or greater, with low pressure drops along a streamlined flowpath having substantially no stagnation point. Low pressure drops and substantial elimination of stagnation points are achieved by having smooth transition points where different elements of the device abut (e.g., the channel-catheter interface) and by having all changes in lumen diameter be of a gradual nature and having straight or nearly straight flowpath without sharp curves or objects protruding into the flowpath and no dead volume.
Because such large flowrates are desired with low resistance, it is necessary to have the largest needle outside diameter that patients will accept. Accordingly, rigidity of the puncture needle is desired. A rigid needle allows a greater inner lumen diameter per outer component diameter (i.e., thinner walls) than does a flexible tube. This is important because it allows the needle to be as small as possible, thereby lessening the trauma on the patient""s puncture site, yet still be capable of handling large flowrates. Flexible tubes have a much higher outer diameter to inner diameter aspect ratios. Thus, to accommodate the bloodflows common during hemodialysis, a much larger outer diameter would be required if flexible materials were used. Also, a rigid needle allows a greater force to be transmitted to the seal to overcome the resistant force generated by the spring. Thus, a greater resistant force can be employed, resulting in a more robust, reliable, and fault-tolerant seal.
Further, the lack of sharp angles or bends in the flowpath is much less injurious to fragile hematocytes. Since the flowpath from needle to catheter (or vice versa) is substantially straight, the turbulence is minimized, and the shear stresses lessened, resulting in less erythrocyte damage and a lowered tendency toward platelet activation.
Finally, it is anticipated that a medically acceptable, waterbased lubricant will be used on the needle exterior, as a diminished device lifespan of 100-150 cycles has been observed when no lubricant is used. Lifespan should be very long when properly lubricated needles are used for each insertion.
Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings in which: